Inflammatory bowel diseases in Faroese‐born Danish residents and their offspring: further evidence of the dominant role of environmental factors in IBD development

Abstract

SummaryBackgroundThe incidence of inflammatory bowel disease (IBD) is record high in the Faroe Islands, and many Faroese emigrate to Denmark, where the IBD incidence is considerably lower.AimTo study the IBD incidence in first‐, second‐ and third‐generation immigrants from the Faroe Islands to Denmark to assess the extent to which the immigrants adopt the lower IBD incidence of their new home country.MethodsData on Faroese‐born Danish residents and their children were retrieved from the Danish Central Population Register for 1980–2014. Incident IBD cases were identified from the Danish National Patient Register. Standardised Incidence Ratios (SIRs) were used to compare the IBD risk in immigrants with that of Danes. 95% confidence intervals (CI) were calculated using the square‐root transform.ResultsFirst‐generation Faroese immigrants had a higher IBD incidence than Danes, SIR 1.25 (95% CI, 0.97–1.59) for men and 1.28 (95% CI, 1.05–1.53) for women. This excess risk derived from ulcerative colitis (UC), SIR 1.44 (95% CI, 1.10–1.87) for men and 1.36 (95% CI, 1.09–1.68) for women. No excess risk was found for Crohn's disease (CD). The UC risk was nearly doubled during the immigrants’ first 10 years in Denmark; SIR 2.13 (95% CI, 1.52–2.92) for men and 1.63 (95% CI, 1.19–2.18) for women.ConclusionsAlthough some impact of genetic dilution cannot be excluded, our findings indicate importance of gene‐environment interplay in UC, as the excess UC risk in Faroese immigrants to Denmark disappeared over time and over one generation in men and over two generations in women.

Marked regional variations in the prevalence of inflammatory bowel disease in a limited geographical region are not associated with compounds in the drinking water

“…The incidence for both CD and UC was rather stable during the fairly long 10-year observation period. The levels are well in accord with those found in other countries within the Western world, that is, with similar environmental circumstances [1,2,4,31]. However, this is in contrast to a recent Danish investigation where the incidence has been steadily increasing over a longer time span for around 50 years.…”

“…This higher risk disappeared over time in Faroese immigrants that moved to Denmark. After 1-2 generations, these immigrants had the same IBD incidence as the people in Denmark [4]. In view of these variations, environmental factors are thought to be of great importance.…”

Editorial: inflammatory bowel disease risk reduction after migration – are early life events important?

“…2 In the current study, Hammer et al determined the IBD incidence of first-, second-and third-generation Faroese immigrants in Denmark relative to the risk in the local Danish population using linked population databases. 4 The Stan- The findings of this study add to the growing body of evidence supporting the complex role of environmental factors in modulating IBD risk. The Swedish population-based study by Li et al 5 and the Canadian population-based study by Benchimol et al 6 suggested that low-risk migrants over subsequent generations adopt the risk of the country to which they migrated.…”

“…We do not know the rate of C. difficile colonisation in the IBD patients. C. difficile carriage is higher in IBD patients 4 so asymptomatic colonisation rates may be more prevalent. It is also likely that most IBD patients admitted with exacerbation would be tested for C. difficile and perhaps more so than for non-IBD admissions.…”

“…4 The Stan- that low-risk migrants over subsequent generations adopt the risk of the country to which they migrated. Consistent with the findings of the present study, our group also demonstrated an increased risk of IBD in migrants from a high incidence region, UK, to Canterbury, New Zealand where IBD incidence had previously been low.…”